I live in Brisbane north. Just my personal opinions:
Zillmere - although there has been improvement still needs a lot of work. Lot of housing commission types wandering around. Not an appealing suburb for owner occupiers. The suburb itself is unappealing, very old. Lots of new townhouses/units going up. Good transport links.
Caboolture - lots of dole bludgers/low socio economic area. You could probably get a cash flow positive place but have to deal with feral tenants. Quite a way from Brisbane but since your tenants probably wont work, not so much of an issue. There are some nicer areas (upper caboolture). Rail link to city. Town centre of caboolture very run down.
North Lakes - fairly long commute into the city (for Brisbane) about 1 hour in traffic but plenty of people do it. New/newish houses, the neighborhoods are nice and appealing, lakes, walkways, urban landscaping. North lakes Westfield, Costco, Ikea coming. A lot of my friends live there and love it. There are a LOT of houses though, and acres and acres of land cleared for more housing. The blocks are small with houses right on top of each other. New rail eventually will link to city.
Chermside: older suburb but much nicer than Zillmere. Quite a few very large apartment blocks going up closer to Westfield, lots of new townhouse developments, older and newer houses mixed together. Hospitals/ Westfield Chermside/ transport hub for bus.
Interesting that Ive noted a number of people commenting about suburb value and its distance to the coast. Not sure that people value that distance as much here in Brisbane (apart from direct sea views). Other Brisbanites may comment further on this.
Cheers, nat